Bi- and multi-specific binding agents are currently being developed for a variety of therapeutic, diagnostic, and research applications. Many such agents are generated by associating antibody components that target different antigens to one another, for example as fusion proteins or by cross-linking of antibody components. Such approaches, among others, have included generating multispecific antibodies by fusion of cells (e.g., hybridomas) that each express a monospecific antibody, chemical conjugation of two or more monospecific antibodies, and/or recombinant DNA technology. However, such methods have not been without limitation.
In particular, recombinant DNA technology has yielded several engineered antibodies that are multispecific and multifunctional. With the advent of single chain Fv molecules, many advances in engineered antibodies have been made. Such engineered antibodies have exhibited improved properties over traditional antibodies due, at least in part, to unique formats that have resulted. Although several strategies exist for engineering multispecific antibody agents, most efforts have focused on improving only certain functional aspects. As a result, most engineered proteins made from antibody components do not possess all the desired functional properties that would confer the most pharmacological significance.